Here is a list of common issues with carbs and the best approaches to identify & solve the problems. Sometimes the appropriate repair does not require carb rebuilding. But first…
Warning – Honda motorcycles and many other brands have Overflow Tubes connected to a drain tip on the float bowls of the carbs. These tubes are routed down by the rear wheel.
You MUST use these tubes – these drain any gas overflow away from the hot motor. Often a starter is lurking in the motor case right below the carbs, with full battery power connected. It’s a perfect setup for a fire if you don’t use those tubes!
Throttle sticks – If you ride off-road, do check that no debris has fallen in by the carb(s) and restricted the movement of the linkage.
Check the handgrip and cables, because if one of these items is the source of the problems, you may not need to rebuild the carbs at all! Here’s how:
Before touching the carbs, ensure that your throttle handgrip and cables are in good condition. The assembly is usually made in halves which incorporate start/stop switches. The halves are held together with two bolts or screws. Always disconnect the battery when doing the following, to avoid accidental electrical short circuits.
Note – Many clutch and throttle assemblies include a small pin which aligns with a hole in the handlebars, to stop the assembly from turning. When removing the assembly, watch for the pin which may be part of a small metal tab that locates into the plastic assembly and is easily lost. Upon reassembly, make sure the pin is properly located on the handlebars. Otherwise, you may crack the plastic parts as you tighten the fasteners.
Remove the fasteners and carefully separate the halves. Inspect for dirt and debris. It’s amazing how many times you’ll find cobweb material inside. Use low pressure air to blow out debris. Do not use lubricant in any throttle assembly with incorporates electrical switches or the lube may cause electrical problems. You can clean the electrical contacts with common electrical contact cleaner spray.
Disconnect the throttle cable(s) and remove them from the handgrip, then reassemble the grip on the handlebars. Check that the throttle assembly is free to move throughout it’s rotation without any indication of sticking. If you cannot identify the source of the problem or if you cannot fix it, then replace the assembly.
Remove the gas tank, because to check the cables, that tank needs to go! Once it is removed, check the condition of the cables, looking for chafed or kinked outer covers. If the outer cover is chafed, moisture can get inside and promote corrosion. Check too that the cables are routed in the smoothest curves to avoid binding and ensure they are routed well into their mounts at the carbs. If they reach the carbs and the inner cable comes out of the outer cable at an angle, the inner will chafe and cut into the outer housing, causing the throttle to stick. If a cable housing has a groove cut in it by the inner cable, replace it. Just rerouting it may temporarily stop it from sticking but there’s a real risk that it may unexpectedly stick later.
Move the carbs’ throttle linkage and see if the cables move freely. No go? Try pulling the free ends of the cables out of their position on the bike, so you have them laid straight out from the carbs. Now you should be able to slide the cable’s outer housing on the inner. If it doesn’t slide freely, you can try lube them, but note that jammed cables are not often fixed with lube. If lubing causes the cable housings to slide freely on the inner cable, you can lay them back in place on the bike, connect to the grip and try again.
If still no joy, chances are good that the carb linkage may be sticking which still does not demand a carb rebuild yet. Start by spraying the exposed carb linkage with penetrating lube like WD40 and try to loosen the linkage by gently prying with a screwdriver. Be careful not to bend any of the metal linkage parts. If no joy, remove the carbs and rebuild them.
See Carb Remove & Replace
Carb Leaks:
Leaks can be caused by relatively simple issues such as bad O ring seals on float bowl drains, cracks in the float bowl itself or it’s overflow tube (on Keihin carbs used on Hondas), bad float bowl gaskets, improperly tightened float bowl screws or spring clamps.
Leaks can also be caused by issues that generally require carb tear-down, like sunken floats or dirty float needle seats. Though it is possible to replace floats on a bike at times, setting the correct float height is not easily done on the bike.